Why does this constructor not return a string?

Question

Consider:

function Panda() {
   this.weight = 100;
   return [1,2]; 
}

console.log(new Panda());

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When we create an instance with the keyword new( new Panda()), it returns:[1,2]

Without a return statement, it returns: { weight: 100 }

function Panda() {
   this.weight = 100;
}

console.log(new Panda());

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Using the return statement: return "Hello"it returns{ weight: 100 }

function Panda() {
   this.weight = 100;
   return "Hello"; 
}

console.log(new Panda());

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Why is he doing this? Because it must be an object?